Behavioral Health denial code (Updated for 2026)

Common Causes for CO 256

Denials with code CO 256 typically happen for the following specific reasons:

• The patient's behavioral health benefits are carved out to a separate Managed Behavioral Healthcare Organization (MBHO) instead of the primary medical insurer.
• Failure to submit the claim to the correct dedicated behavioral health claims billing address or payer ID.
• Lack of required prior authorization from the specific behavioral health TPA before rendering psychotherapy or intensive outpatient services.
• The rendered behavioral health CPT code is excluded from the employer group's specific benefit plan design.

How to Prevent CO 256 Denials

To avoid receiving this denial in the future, implement these specific checks:

• Perform comprehensive eligibility and benefit verification prior to the first visit to identify any carved-out behavioral health plan administrators.
• Ensure the billing team routes behavioral health claims to the correct TPA or MBHO payer ID rather than the primary medical carrier.
• Obtain explicit prior authorization from the designated behavioral health carrier whenever required by the patient's employer plan.
• Implement automated billing system rules that flag behavioral health CPT codes for manual routing review based on the patient's specific group ID.

Appeal Letter Template for CO 256

If you believe this claim was denied incorrectly, you can use the following template to submit an appeal.

[Your Practice Header]
[Date]

[Payer Name]
[Appeals Department Address]

RE: Appeal for Claim [Claim Number]
Patient: [Patient Name]
ID: [Patient ID]
Date of Service: [Date]
Denial Code: CO 256 - Behavioral Health denial code

Dear Appeals Department,

I am writing to appeal the denial of the above-referenced claim, which was denied with code CO 256: "Behavioral Health denial code".

We are appealing the denial of claim number [Claim Number] under code CO 256. The behavioral health services rendered, specifically CPT code [CPT Code], were medically necessary and directly aligned with the patient's documented diagnosis of [ICD-10 Code]. Under the Mental Health Parity and Addiction Equity Act (MHPAEA), financial requirements and treatment limitations applied to mental health and substance use disorder benefits cannot be more restrictive than those applied to medical and surgical benefits. The submitted clinical documentation demonstrates that all criteria for coverage were met, and any required coordination with the designated behavioral health administrator was performed. We request a thorough review of this claim in compliance with federal parity guidelines and ask that payment be processed to the appropriate behavioral health benefit administrator.

Attached please find:
1. A copy of the original claim.
2. The relevant medical records supporting the service.
3. [Any other supporting documents].

We respectfully request that you reprocess this claim for payment.

Sincerely,

[Your Name]
[Title]
[Practice Name]